Prioritization of Annual Mains Replacement Activities Using Historical Failure Data, Hydraulic Modeling, and Economic Data

Water utility operations and engineering staff are responsible for the integrity of water distribution mains, including the development of a capital improvement program that ensures replacement and rehabilitation activities are targeted for best value. The City of Atlanta used a capital planning approach towards mains replacement activities that was developed by Advantica, Inc. using predictive condition modeling based on historical main failure data. The approach weighted this data using hydraulic modeling results to determine current levels of service for each main, targeting mains for replacement that were critical to meet Atlanta's service-level goals, which consider social, economic, and environmental factors. The predictive condition model calibrated by Advantica was based on historical pipe breakage data and the material and age of each system pipe. This condition model was built within Atlanta's GIS system using a specialized application to perform a statistical analysis of the failure data and predict future pipe failures. Atlanta also wished to consider key performance indicators from its distribution network hydraulic model and target pipes for replacement that were poor performers in providing adequate fire flows throughout the system. Atlanta's distribution network model was used to analyze each pipe in the system and determine the number of times it constrained the system in meeting required fire flow demand. Advantica used a weighted analysis to rank mains for replacement considering the condition model and the hydraulic performance indicators. A total score was derived for each pipe in the system based on the sum of the weighted values of each indicator and the pipes were ranked according to this total score. The ranked mains were then grouped into regional projects to match the City's target level of expenditure while also gaining cost efficiency by considering other utility and excavation projects and other non-technical factors (i.e. social, economic, and environmental) affecting regional utility improvements.